Technical Field
The present invention relates to a rotor for a rotary electric machine which is installed in a vehicle such as a hybrid car and an electric car and is used as a motor and a generator.
Related Art
A revolving-field type synchronous motor (hereinafter, referred to as “IPM motor”) is known as a rotary electric machine which is installed in a vehicle or the like. The IPM motor has a structure in which magnets are buried in a rotor. Since the IPM motor can utilize reluctance torque produced by magnetization of the rotor and torque produced by magnetization of the magnets, the IPM motor operates at high efficiency. Hence, the IPM motor has been appropriately employed for a hybrid car, an electric car and the like.
Such an IPM motor includes a stator and a rotor, which is disposed so as to be opposed to the stator in the radial direction. In addition, a rotor is known which includes a rotor core and a plurality of pairs of magnets. The rotor core is formed by laminating a plurality of steel plates in the axial direction and crimping the steel plates. The rotor core has a plurality of pairs of magnet housing holes disposed in a V shape so that the distance therebetween increases toward the stator. Each pair of magnets is housed in the pair of the magnet housing holes to form a magnet pole.
JP-A-2011-211860 discloses a technique for providing a central barrier (flux barrier) serving as a magnetic air gap on a d axis of a rotor core to obtain reluctance torque by increasing the difference between d axis inductance and q axis inductance. JP-6-284649 discloses a rotor core and a manufacturing method thereof, the rotor core being formed by cramping a plurality of steel plates laminated in the axial direction.
According to the structure of the rotor disclosed in JP-A-2011-211860, the d axis inductance can be decreased, and flux leakage to the central barrier can be suppressed. However, when large centrifugal force is caused, the force for cutting out the rotor becomes large.
When the rotor core formed by laminating a plurality of steel plates in the axial direction is fixed by using the technique disclosed in JP-6-284649, stress concentration is caused between the cramping portion and the central barrier. In this case, great stress concentration is caused due to the influence of centrifugal stress and heat stress caused by the difference between coefficients of linear expansion of the rotor core and the magnet.